1. Field of the Invention
This invention relates to a stereoscopic image display device capable of tracking a head position of a viewer and ensuring perception of a stereoscopic image by the viewer without using special glasses.
2. Description of the Prior Art
A parallax barrier system and a lenticular lens system are well known as methods for displaying a stereoscopic image without special glasses. When these systems are used for structuring a stereoscopic image display device autostereoscopic image display device, the display device is generally structured so as to be a two-eye system because of limited resolution of a liquid crystal panel. The device of the two-eye system displays an image for a right eye and an image for a left eye on every alternate vertical line on a liquid crystal display panel 200 as shown in FIG. 1. A lenticular lens and a parallax barrier (not shown) are structured so that a viewer 2 in an optimum viewing position D can observe an image for a right eye and an image for a left eye alternately with a pitch of an interval between pupils E.
In FIG. 1, R, R1, R2, R3, R4 . . . are areas for perceiving an image for a right eye, and L, L1, L2, L3 . . . are areas for perceiving an image for a left eye. When a right eye of the viewer is in the area for perceiving an image for a right eye and a left eye of the viewer is in the area for perceiving an image for a left eye, the viewer can percept a stereoscopic image. An image from a whole surface of a screen corresponding to an eye is focused in the area for perceiving an image in each of the eyes. Thus, as shown in FIG. 3, taken the R2 area in exact front of the screen as an example, a position shifted in back and forth directions a little in the R2 area can be the area for perceiving an image. The image for a right eye reaches from the whole screen to a square shaped area G, and thus the viewer can observe the image for a right eye even when being in a position of an upper or lower end of the square shaped area G. Light passing through the R2 area reaches only in a shaded area of the figure.
In accordance with the above principle, areas for perceiving an image for right and left eyes are indicated as square shaped (shaded) areas shown in FIG. 4. Therefore, as shown in FIG. 5, when the right eye of the viewer 2 is in the square area for perceiving a right eye image and the left eye of the viewer 2 is in the square area for perceiving a left eye image, the viewer 2 can perceive a stereoscopic image. On the contrary, when the eyes of the viewer are not in the above areas, the viewer can not perceive a stereoscopic image.
As a method for enlarging an area for perceiving a stereoscopic image, as disclosed in JP 9-152668, A (IPC: G03B 35/00), an image for a right eye and an image for a left eye displayed on the liquid crystal display panel 200 are replaced when a position of the viewer 2 is detected and it is found that the viewer 2 is in a reverse view area where the image for a left eye is in the right eye of the viewer and the image for a right eye is in the left eye of the viewer. In JP 9-197344 A (IPC: G02B 27/22), a liquid crystal panel or the like is used wherein a shading barrier or a parallax barrier having an aperture of an aperture shape arranged between the liquid crystal display panel and a backlight shifts by a ¼ pitch of a pitch of the shading barrier or the parallax barrier (barrier shifting). In this structure, the square areas shown in FIG. 4 shift by E/4 and each image can be observed in an outline square area, as shown in FIG. 6. That is, the areas for perceiving a right eye image R, R1, R2, R3, R4 . . . become R′, R1′, R2′, R3′, R4′ . . . and the areas for perceiving a left eye image L, L1, L2, L3 . . . become L′, L1′, L2′, L3′ . . .
Thus, a stereoscopic image can be supplied on a boundary area of the right eye image and the left eye image in back and forth directions before barrier shifting. The right eye image and the left eye image can be observed and an area for perceiving a stereoscopic image is enlarged in any positions of the shaded square areas and the outline square areas in FIG. 6 by optimally controlling replacement of the right eye image and the left eye image displayed on the liquid crystal display panel 200 and shifting of the barrier and the shading plate.
In the above structure, however, stereoscopic view is not ensured when the viewer shifts a great distance backward as shown in FIG. 7. In FIG. 8, a left eye image passing through L1 from an area 2 of a liquid crystal display panel 200, a right eye image through R2 from the area B, and a left eye image through L2 from the area C are perceived by a right eye of the viewer 2, thus the viewer perceives a moiré on a boundary of the areas A, B, and C on a display surface. This is equivalent to a boundary between the areas L1, R2, and L2. Therefore, when the viewer 2 shifts a great distance in back and forth directions from a position capable of viewing a stereoscopic image, the viewer 2 perceives both of the right eye image and the left eye image, and stereoscopic view is not ensured.